This invention concerns a vernier-type electrodynamic machine.
A machine of this type is known, comprising two parts separated from one another by an air gap arranged along a surface, said parts being operable to move relative to one another in one direction of said surface such that the width of the air gap is kept constant,
the first of said parts consisting of a magnetic armature with N teeth forming N slots opening onto the air gap and being evenly distributed along said direction,
the second part comprising M elements arranged along said direction, M being a whole number different from N, said elements being operable, due to the difference between M and N, to create shifts within the air gap relative to the armature teeth, said successive shifts varying along said direction according to a linear mean law, and means for creating in said gap a multipolar magnetic field,
and means cooperating magnetically with the armature to create within said gap a magnetic field of the same polarity as the previous filed, said second field sliding along said direction in relation to the armature, said shifts bringing about a difference between the sliding speed of the sliding field and the speed of one part relative to the other when said two previously mentioned fields move synchronously.
Several specific forms of vernier-type electrodynamic machines known in the prior art are described below by way of example, with reference to the first half of the appended drawings in which:
FIG. 1 is a partial longitudinal cross section of a known vernier-type motor;
FIG. 2 is a partial cross sectional view showing the stator and rotor tooth outline of the motor illustrated in FIG. 1;
FIG. 3 is a partial cross sectional diagram of another known type of vernier motor;
FIG. 4 is a graphic representation of the operation of the motor partly outlined in FIG. 3;
FIG. 5 is a partial cross sectional diagram of a known vernier-type speed reducer; and
FIG. 6 is a partial cross sectional diagram of another known vernier-type speed reducer.
The vernier-type motor illustrated in FIG. 1 comprises a stator 1 with a winding 2. The stator 1 is made from an assembly of tooth-edged magnetic plates and the winding 2, a 2 p pole polyphase design, is wound in the slots between the stator teeth. The stator 1 is an annular, cylindrical body of revolution about an axis 3. A toothed rotor 4, also made from magnetic plates, is mounted rotatably about axis 3, is positioned within the internal cylindrical volume of stator 1 and is separated from the latter by a cylindrical air gap 5. A cylindrical magnet 6 is coaxially fitted in rotor 4. It is fastened therein so that one flat end 7 of the magnet is within the volume of the rotor 4 and the other flat end 8 is located outside said volume. Magnet 6 is magnetized in direction 9, going from end 8 to end 7, such as to set up in rotor 4 a magnetic flux crossing air gap 5 and penetrating into the stator 1. Said stator is attached to the inside of a cylindrical magnetic shell 10. Rotor 4 and magnet 6 are attached to a shaft 11 rotatable about axis 3 in two bearings supported by the shell 10. The end bell 12 shown in cross section in FIG. 1 comprises a ball bearing 13 for shaft 11. This end bell 12 is made of magnet steel and comprises a surface 14 disposed near and facing end surface 8 of magnet 6 such as to close the magnetic circuit created by magnet 6.
As shown in FIG. 2, the stator 1 teeth are evenly spaced around the axis of the machine. Said stator has n equal slot pitches per pair of poles as defined by the winding 2. The rotor 4 teeth are also evenly spaced around the axis of the machine, but the rotor has more teeth than the stator; rotor 4 for example may have n+1 teeth per pole pair. The rotor's position relative to the stator in FIG. 2 is such that one side of a tooth 15 on the rotor is aligned with one side of a tooth 16 on the stator according to a radial direction 17. As is apparent, the following teeth 18, 19, 20 of the rotor are offset in relation to their matching teeth 21, 22, 23 on the stator. These staggerings have a magnetic effect in the gap 5 traversed by the magnetic flux from magnet 6.
When the winding 2 is supplied with polyphase current, it sets up a revolving field about axis 3. The motor depicted in FIGS. 1 and 2 is a homopolar sychronous design. The magnetic flux created by magnet 6 must revolve at the same speed as the revolving field. Due to the staggering mentioned above, the rotor rotates at a slower speed equal to the quotient of the speed of the revolving field and a coefficent K.
In the case where the stator has n teeth per pair of poles and the rotor n+1 teeth per stator pole pair, said coefficient K equals n+1. This speed reduction is accompanied, unlike in a common synchronous machine with the same continuous field flowing through its armature, by an increase in torque, said torque being multiplied by said K factor.
It is possible however to make vernier-type machines according to the prior art in which the successive staggering steps each correspond to several slot pitches. For example, in the motor represented in FIG. 3, the rotor 24 has evenly spaced slots, while the stator 25 has groups of slots, each of which groups is separated from the next by an interval. Each group comprises several slots spaced equally both with respect to each other and with respect to the rotor slot pitch. The figure shows a first group of stator slot pitches comprising teeth 26, 27 and 28 and a second stator group comprising teeth 29, 30 and 31. These two groups are separated from one another by an interval 32 able to accommodate a stator coil bundle 33.
In the position represented in FIG. 3, teeth 26, 27 and 28 are exactly aligned with rotor teeth 34, 35 and 36. Interval 32 is determined to provide a staggering such as 37 between stator teeth 29, 30 and 31 and rotor teeth 38, 39 and 40.
FIG. 4 graphs the law of variation 41 of the offsets along the air gap in the type of machine illustrated in FIG. 3. The position along the gap is plotted on the X-axis in terms of an angle A in relation to a reference axial plane and the offsets D are plotted on the Y-axis. It can be seen that curve 41 includes successive plateaus 42, 43, 44 and 45. Based on this law of step changes, it is possible to define a linear mean law 46.
In practice the two constructional types of vernier motors represented in FIGS. 2 and 3 operate the same way.
The operating principle for vernier-type electrodynamic machines also applies to vernier-type generators, in which case the rotor of the machines represented in FIGS. 2 and 3 is made to rotate, for example, and the electric current generated in the stator coils of these machines is collected.
The same principle also applies to linear vernier-type machines in which the air gap is not arranged along a cylindrical surface but along a plane surface separating the two relatively moving parts; the moving part then moves relative to the stationary part along a straight path parallel to the air gap surface.
It is further possible to make vernier-type electrodynamic machines which operate as rotary reducers.
The prior art reducer represented in FIG. 5 comprises a first, annular shaped rotor 47. This rotor has no teeth but carries a continuous winding 48 with 2 p poles. Said reducer further comprises a second, cylindrical and coaxial rotor 49. The latter rotor has teeth, not shown in the drawing, which are identical to those of the motor rotor of FIG. 2. Between said rotors 47 and 49 an annular shaped stator 50 is provided and coaxially mounted, having n radial teeth 51 per pole pair, said teeth being separted from one another by spacers 52 made from an amagentic material. Cylindrical air gaps 53 and 54 separate rotors 47 and 49.
When the rotor 47 is rotatively driven at a speed v and the winding 48 is supplied with direct current, this sets up a revolving field which radially crosses the stator 50 and penetrates the second rotor 49. It is thus apparent that the assembly 47-53-50 is the equivalent of the stator in the motors of FIGS. 2 and 3. Under these conditions, if rotor 49 has n+1 teeth per pole pair of winding 48, then rotor 49 rotates at a speed of v/n+1.
Still another prior art vernier-type reducer is illustrated in FIG. 6, comprising a stator 55 and a rotor 56, arranged coaxially and both having teeth. The revolving field is produced in this case by another coaxial rotor 57 located in the air gap between stator 55 and rotor 56. Rotor 57 comprises 2 p magnets such as 58, which are juxtaposed along the air gap and whose radial directions of magnetization 59 and 60 alternate to create a revolving field with 2 p poles. If the stator 55 has n slots per pole pair and the rotor 56 has n+1 slots per pole pair, driving rotor 57 at a speed v causes rotor 56 to rotate at a speed v/n+1.
Consequently, as a rule, the vernier-type electrodynamic machines of the known art are homopolar, synchronous types of machine whose two relatively moving parts each comprise a set of teeth, said sets of teeth facing one another and the number of teeth in one set being different from the number of teeth in the facing set.
There are disadvantages with these machines. In particular, they must be provided with a narrow air gap in order to enhance the vernier effect provided by the staggering of the teeth. This cutting back on the air gap entails, due to the saturation of the magnetic circuit, a decrease of the number of ampere turns and consequently of the machine's torque. Moreover, the mgnetic flux of these machines includes a homopolar component which contributes to saturating the magnetic circuit, without producing any torque. This results in undue bulkiness which may preclude the use of these machines for some applications.
The present invention is directed to obviating these drawbacks.
The invention provides a vernier-type electrodynamic machine of the kind comprising two parts separated from one another by an air gap arranged along a surface, said parts being operable to move relative to one another in one direction of said surface such that the width of the air gap is kept constant,
the first of said parts consisting of a magnetic armature with N teeth forming N slots opening onto the air gap and evenly spaced along said direction,
the second part comprising either M teeth arranged along said direction and forming M slots with a different pitch form that of the teeth of said first part, or P groups of Q teeth arranged along same said direction and having the same pitch as that of the teeth of said first part, said groups being staggered to yield a vernier effect,
and means for establishing in said air gap a magnetic field sliding relative to said first part along said direction, wherein each of the teeth of the first and second parts comprises magnetic induction generators creating induction fluxes normal to the air gap and oriented in the same direction.